[llvm] Add out-of-line-atomics support to GlobalISel (PR #74588)

[Matt Arsenault via llvm-commits]

================
@@ -758,16 +758,32 @@ AArch64LegalizerInfo::AArch64LegalizerInfo(const AArch64Subtarget &ST)
           all(typeInSet(0, {s8, s16, s32, s64, s128}), typeIs(2, p0)));
 
   getActionDefinitionsBuilder(G_ATOMIC_CMPXCHG)
+      .libcallIf([&ST](const LegalityQuery &Query) {
----------------
arsenm wrote:

the legal cases should be the first cases in any builder 

https://github.com/llvm/llvm-project/pull/74588